Solid oxide fuel cells (SOFCs) are an alternative to traditional combustion engines and turbines for producing energy. Fuel cell technologies may produce electricity with greater efficiency and lower environmental impact and fuel cell technologies generally have lower CO, NOx, and SOx emissions. Solid oxide fuel cells may use natural gas, kerosene, and diesel fuels, among others, as fuel sources. However many typical SOFCs suffer from high costs per unit power output.
Solid oxide fuel cells may be manufactured in several forms, including tubular and planar SOFCs. Each of these forms uses a support structure. Tubular SOFCs typically use a strontium oxide doped lanthanum manganite (LSM) porous support tube. Planar SOFCs may utilize an electrolyte-supported structure or an electrode-supported structure. The electrolyte-supported structure is typically formed of yttria-stabilized zirconia having a high thickness. These thick electrolytes have a high ionic resistance, which results in a reduced cell potential.
Electrode-supported SOFCs may be formed with the cathode or the anode supporting the structure. Cathodes, such as lanthanum strontium manganite (LSM), have coefficients of thermal expansion close to yttria-stabilized zirconia. On the other hand, anode-supported cells are generally formed with nickel and yttria-stabilized zirconia. The coefficient of thermal expansion of the nickel containing yttria-stabilized zirconia is greater than that of the yttria-stabilized zirconia electrolyte. In both the cathode-supported and anode-supported cells, large electrode thickness affects the diffusion of reactants and the resistance of the electrode. In either case of electrode or electrolyte supported cells, the effect of the thick electrolyte or electrode reduces the cell potential or current density, adversely affecting efficiency of the SOFC system.
In addition to the support structure concerns, challenges exist with coupling electrical contacts to electrodes. Typical SOFCs have gas impermeable interconnects. The typical interconnect has a thermal expansion coefficient dissimilar to that of the electrode. Coefficient of thermal expansion differences cause interconnects to shear from the electrode, causing an increase in resistance in the cell. Some interconnect materials diffuse into the electrode structure. Poor construction of interconnects leads to reductions in operational potential and current density.
As such, typical solid oxide fuel cell technologies suffer from deficiencies in structure and manufacturing that increased the cost of energy produced. Accordingly there is a need for improved electrodes, electrolytes, SOFCs, and SOFC stacks.